In an optical communication system, an optical signal is sent from a transmitter to a receiver over an optical channel. At the transmitter, data is received in the electrical domain and the optical signal is generated in accordance with the received data. At the receiver, the data is recovered from the received optical signal.
The data may be encrypted in the electrical domain, prior to being converted into an optical signal. However, an interloper may intercept the optical signal during transmission and convert the optical signal back into data in the electrical domain. The interloper may then try to decrypt the data.
Encryption is performed in the electrical domain, and both encryption and decryption of data carry a computational cost. Service providers wishing to provide a secure channel must either ensure that their customers are using encryption, or they must do bulk encryption and decryption at either end of a channel. Service provider customers may not be sufficiently sophisticated to ensure all communications are encrypted, and the cost of doing bulk encryption is not attractive to many service providers.